AC High side low pressure switch

87 xj12, I bought a new high low pressure switch when my mechanic found that the original to have failed.
when I tried to fit it the upper crimped shoulder is higher than the groove that the cir-clip fits into.
When I search for these switches they all look the same with the crimped top.
Has anyone had similar experience, or do you know of a supplier with a switch that its?

Are you sure that you originally have high side pressure switch? I think in 87 low side switch was still used. Or did you change the head and upgrade to high side low pressure switch?

I thought I had it correct, I’ll have to check!!

1987-ish was when the change from “Superheat Switch” to “HSLP Switch” (high side low pressure) occurred. I think the VIN break was something like 470xxx but don’t take that to the bank

Assuming no previous mods or hatchet jobs…

If you see a small, square-ish, three-terminal thermal fuse in the wiring near the compressor, you have the “superheat” system. If not, it’s the HSLP system.


Well son of a gun, I had been going down the low pressure switch path as a result of a diagnosis of a mechanic that looked at it when it was still on the road, (long time ago now). However on Doug’s advice I checked and I have the super heat system.
I noted elsewhere that if the fuse is working there should be continuity between the 3 poles which I’ll check but is it possible the sensor in the back of the compressor is faulty? How does one check that?
It will be a while before it is all back together to test while running, but if I can check a few things now that would be good.
Thanks Doug

The superheat system delivers power from green/brown through green to the compressor clutch, Dave - through a fuse between the two.

However; the sole purpose of the sensor at the back of the compressor is to provide ground, black wire for the heating coil (powered from green) - to blow the thermal fuse with overheating compressor. Any failure of the sensor should either simply blow the fuse - or not interfere with the power to the compressor clutch…

Ie, thermal fuse working as it should will indeed show continuity between all the three (C,B,S) connections. However; it is important that the fuse is disconnected when ohming. With a blown fuse; there is continuity between S (black) and C (green) - but ‘break’ between either and B (green/brown)…

The functional test of the compressor clutch is to jumpwire 12V to green at the clutch - it should then engage audibly…

As an aside; in this set-up, the clutch has a permanent ground. With the pressure switch set-up; the clutch is powered - and ground is though the pressure switch. Which breaks ground at low pressure…

xj6 85 Sov Europe (UK/NZ)

I believe that I had this problem. My compressor still kicked on despite I had no refrigerant. The superheat fuse should blow within 6 minutes of the compressor coming on if there’s no refrigerant if the fuse is good and the switch is good.

As you already have a new high side low pressure switch I would recommend upgrading your compressor to this setup. You will need a new compressor head and redo the wiring, but it is a better setup. New heads (part number: JLM1041) are really cheap and available from Jaguar or other suppliers like SNG Barratt:

thanks John, my superheat fuse is definitely blown.
I’m going to look into making the switch as you recommend above.